The long-term goal of this program is to characterize structural biochemistry related to DNA adduct-induced frameshift mutagenesis. Adduct- induced mutagenesis is believed to be the initiating step within a complex cascade of events leading to chemical carcinogenesis. Frameshift mutations could cause the inactivation of tumor suppressor genes, and thus be important in mediating chemical carcinogenesis. Working with adducts for which mutagenic data is available, testable mechanistic hypotheses are being developed regarding the structural origin of specific mutations. These are examined using modified oligodeoxynucleotides designed to model specific structures. NMR spectroscopy is the primary technique used to derive detailed structural information. The behavior of adducts will be examined within the context of an iterated repeat sequence derived from the hisD3O52 mutation of Salmonella typhimurium, where frameshift mutations are known to occur. Oligodeoxynucleotides modified with the 1,N2-pyrimidopurinone adduct of guanine M1G, aflatoxin B1, benzo[a]pyrene, and N-acetylaminofluorene and aminofluorene will be constructed and examined. The primary lesions will he compared with the corresponding unpaired adducted nucleotides in which the lesions form part of the bulge. Experiments on a palindromic frameshift-prone sequence from the hisD3O52 gene will be initiated. The goal will be to determine how adducts perturb the equilibrium between duplex and hairpin loop conformation, and to examine the structures of each. Initially 1,N2-propanodeoxyguanosme and M1G will be examined. Subsequent work will focus on the bulky adducts benzo[a]pyrene and aflatoxin. The propensity of aflatoxin B1 adducts to act as aberrant templates will he examined, building upon observations that incorporation of an extra adenine opposite aflatoxin stabilized the DNA duplex. Aflatoxin B1 will be incorporated into oligodeoxynucleotides in which the aflatoxin moiety is opposite an extra cytosine in the complementary strand. A unifying theme is the concept that DNA adducts can equilibrate between multiple conformations, with the equilibrium distribution dependent upon both adduct structure and DNA sequence. Each conformation can potentially lead to a unique mutagenic event.